Lap and lap holder



' Sept. 2, 1947. w, A, LUTHER 2,426,699

' LAP AND LAP HOLDER Filed July .15, 1944 INVENTOR.

WILL [HM 4.1 11mm.

A TTOR NE Y5 Patented Sept. 2, 1947 LAP AND LAP HOLDER William A. Luther, Croton Falls, N. Y., assignor to Bard-Parker Company, Inc., Danbury, Conn, a corporation of New York Application July 15, 1944, Serial No. 545,113

4 Claims.

My invention relates to improvements in lapping tools particularly tools for lapping holes in metal parts. The function of such tools is to bring a rough hole to exact size in the order of five ten thousandths to five hundred thousandths of an inch (.0005 to .00005") with a smooth or mirror finish. The lapping tool of the present invention comprises a mandrel or lap holder parted in two sections with an angular splice joint between them, and a lap in the form of a split cylindrical sleeve, slid over the joint of the mandrel, and expandible cylindrically as the parts of the mandrel are moved toward each other thus obviating tapered or conical or bell-mouthed holes. I provide means to prevent rotation of the lap on its holder, as for example, a radial inturned flange on the sleeve extending within a slot on the mandrel.

In the accompanying drawing I have illustrated a preferred embodiment of my invention. In these drawings, Figure 1 is a side elevation of the lap-supporting mandrel, showing the lap or sleeve mounted thereon in its initial .or unexpanded position (the sleeve is shown in section) Figure 2 is a transverse section on an enlarged scale taken along line 22 of Figure 1; Figure 3 is a transverse section similar to Figure 2, but showing the sleeve expanded; Figure 4 is a top view of the assembly shown in Figure 1; Figure 5 is an exploded view of the assembly with the parts shown partly in section; Figure 7 is a transverse section through the short section of the mandrel taken along line 'l-'| of Figure Figure 6 is a transverse section through the sleeve taken along line 6-5 of Figure 5, and Figure 8 is a transverse section through the long section of the mandrel taken along line 88 of Figure 5.

The mandrel or lap holder shown in these drawings comprises a long section I and a short section 2. The inner ends of these sections are ground away at a slight taper so that when assembled, as shown in Figure 1, the mandrel is parted in two sections with an angular splice joint between them. The angle of this joint may be varied, but I have found 2 to be satisfactory. Mounted over the tapered end of the long section I is a split cylindrical copper lap or sleeve 3. This sleeve is provided with an inturned radial flange 4 extending within a slot 5 in the tapered end of section I. This tapered end is also provided with a shoulder 6 against which the sleeve abuts and which limits the movement of the sleeve toward the end of the mandrel.

After the sleeve 3 has been mounted upon the tapered end of the large section I, the tapered end of the small section 2 is inserted within the sleeve, the fiat pieces of the sections in contact, until its extreme end reaches the end of the sleeve adjacent the shoulder 6, as shown in Figure 1. In this position the tapered ends of the two sections complement each other to form a cylinder which completely fills the sleeve 3. Now as the two sections of the mandrel are pushed together they will more than fill the sleeve, as shown in Figure 3, and thus cause it to expand. The sleeve 3 acts to hold the sections of the mandrel together in all adjusted positions.

When the lap sleeve and mandrel have been assembled, as shown in Figure 1, the exterior surface of the lap is smeared with a mixture of oil and an abrasive, which may be diamond dust, any one of the aluminum oxides, or other fine abrasive. The end of the long section of the mandrel is then placed in a chuck in a rotating spindle and the lap rotated inside the hole to be lapped, the Work being indicated in broken lines in Figure 1. Meanwhile the projecting end of the short section 2 may be gently tapped inwardly from time to time without stopping the rotation, thus causing the diameter of the lap sleeve cylinder to expand progressively within the hole being lapped. As the lap expands cylindrically, tapered, conical or bell-mouthed holes are avoided. The abrasive dust impregnates the soft copper of the sleeve and acts to abrade or lap the inside of the hole. By longitudinally reciprocating the article to be lapped over the copper lap the hole may be brought to size with extreme accuracy and with a mirror finish.

When the copper lap sleeve is worn, it may be discarded and replaced.

I claim: I

1. An adjustable lapping tool comprising a mandrel parted in two sections with an angular splice joint' between them, a split expandible lap sleeve on the mandrel over the joint holding the sections together in all adjusted positions, and means for preventing rotation of the sleeve on the mandrel.

2. An adjustable lapping tool comprising a mandrel parted in two sections with an angular splice joint between them, a longitudinal slot in one of the sections, a split expandible lap sleeve on the mandrel over the joint holding the sections together in all adjusted positions, and a radial flange on the sleeve lying within the slot.

3. An adjustable lapping tool comprising a split expandible cylindrical copper lap sleeve, and

a cylindrical mandrel parted in two sections with an angular splice joint between them and filling the slot; the sections of the mandrel being slid-able 2,42e,c99 i 7 toward each other to expand the sleeve cylindrically, the sleeve holding the sections together in all adjusted positions. 7

WILLIAM A. LUTHER.

REFERENCES CITED The-following references are of record in the file of 5' this: patent:

UNITED STATES PATENTS Name Date Number s I Groetchen June 16, 1936 

